1. Field of the Invention
The invention relates to a pump for conveying cement, of the kind having a number of pump cylinders and reciprocating pistons, an input container and a multi-limb oscillating shutter valve arranged in front of the pump cylinders and below the input container, the housing of which valve features two pressure inlet ports connected alternately to the associated pump cylinders respectively, an outlet and a suction inlet, the multi-limb oscillating shutter being arranged on a horizontal shaft to be movable between two positions and having a lower outlet control limb passing over the outlet.
2. Description of the Prior Art
Because of the properties of cement, cement pumps suffer to a relatively large extent from the danger of interruptions in delivery. For this reason, in particular, measures must be adopted with the oscillating shutter valve to prevent gradual blocking of the valve ways with setting cement. Furthermore, such pumps must often be installed on vehicles. Thus, a compact construction of the oscillating shutter valve is necessary.
A cement pump is known the valve of which features a two-limbed oscillating shutter the limbs of which are so compact that the rear edges of the oscillating limbs running transversely to the axis of the shaft pass by one or other of inlet ports in the rear side of the housing on changing position as shown in U.S. Pat. No. 4,057,373. An oscillating shutter of this kind has a relatively low-profile construction and has also the advantage that the deflection of the stream of delivered material, as it passes from the respective pressurizing cylinder into the outlet arranged in the end wall of the housing, is small. Thus, the desired low resistances to flow can be be achieved. It is, however, a disadvantage that the pressure channel enclosed by the two limbs, as has been shown in practice with such a pump, forms partial cross-sections which are not, or only inadequately, subjected to flow. Delivery interruptions are traceable back to this, brought about by gradual blocking of the pressure channel by setting cement.
Furthermore, a cement pump is known of the kind first referred to in U.S. Pat. No. 3,588,294 . In this pump, the inlet ports are in the end wall of the housing, the outlet must, on the other hand, be arranged in the floor of the housing so that the two-limbed oscillating shutter passes by this port with the longitudinal edge of its output control limb parallel to the axis of the shaft, and the other control limb can control an inlet port arranged below the input container, on changing position. With this design, very abrupt deflections are produced with very small radii of curvature, especially for the stream of cement coming from the delivery cylinder and arriving in the outlet and for diverting of this stream from the outlet into the connecting end of the delivery pipe.
Furthermore, there results from this a low floor clearance because the oscillating shutter valve housing stands relatively high, owing to the deep position of the delivery pipe connection in the floor of the housing.
If the outlet port is arranged on the end wall of the housing of a two-limbed oscillating shutter of this type, then a considerable increased constructional height results because the angle of swing of the oscillating shutter must not be too large and, for this reason, its pivot axis has to be moved upwards. Because of this, however, the radial extension of the oscillating shutter limbs is correspondingly increased, which applies to the limbs controlling the outlet port and the inlet port, so that the constructional height is doubly increased.
In a further known design (German Pat. No. 1,945,483), for avoidance of the increased constructional height of a two-limbed oscillating shutter, the two limbs are angled towards each other and the outlet port is at least partly arranged in the end wall of the housing. This design has, however, the same disadvantages described earlier, as the designs with one pressure channel.
The essential task of the invention is to effect the control of the flow of cement with a oscillating shutter valve whose flow paths are subjected to flow alternately with cement under suction and pressure and with which the possibility is provided of keeping the constructional height of the valve housing, as well as the height of the input container, low.